Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $60.67   4.491%   $63.3947   $63.39   $63.40   $63.40  
  Purchase #2 $206.41   6.233%   $219.2755   $219.28   $219.30   $219.30  
  Purchase #3 $75.69   7.719%   $81.5325   $81.53   $81.55   $81.50  
  Purchase #4 $191.33   9.793%   $210.0669   $210.07   $210.05   $210.10  
  Purchase #5 $72.84   13.509%   $82.68   $82.68   $82.70   $82.70  
  Purchase #6 $53.99   11.699%   $60.3063   $60.31   $60.30   $60.30  
  Purchase #7 $82.58   4.151%   $86.0079   $86.01   $86.00   $86.00  
  7 purchase totals = $743.51       $803.2638   $803.27   $803.30   $803.30